the peculiar massing of branches, nor are their ultimate articles so readily detached. Perhaps more interesting than all these is the little half-viny Opuntia leptocaulis, with stems, of scarcely the thickness of a lead pencil, interweaving among the branches of some companion plant, usually the creosote bush. It is never to my knowledge found growing except in the immediate proximity of another plant, and thus often escapes detection. It is not very well supplied with spines, and might easily be destroyed by trampling if away from the company of a plant of sturdier growth. Perhaps this is the reason why it usually is so found—it is stamped out elsewhere. Or possibly it needs the partial shade afforded it. This is a question worth an answer.
If you travel for a distance in any direction, other plants will be found. Among these are sweet-smelling acacias, ungraciously, but, I fear, not undeservedly, called cats-claws, with their finely divided leaves and small yellow pompons of flowers. The low leafless shrub Ephedra, with its vertical green stems which look like the scouring rush and is as rough and hard to the touch, is another—a typical desert plant if ever there was one. This plant is a relative of our yew, but is possessed of very unique characters, the description of which would take us too far into details.
Here and there a 'salt' or 'alkali' spot is to be found. Here grow few enough plants, and these such as can endure the hardships of a most unfavorable soil, as for example Atriplex and Dondia. Near the water courses, from which for the greater part of the year water is conspicuously absent, one finds, on the other hand, larger shrubs and very small trees of Acacia, mesquite (Prosopis velutina) and a species of palo verde (Parkinsonia). Ten miles south of Tucson, near to the mission of San Xavier del Bae, the river bottom is occupied by a veritable forest composed wholly of large mesquite, and this the Papago Indians of the region draw upon chiefly for wood. I should mention the presence in parts of the mesa of the many low shrubs which are noticeable chiefly for their inhospitable thorniness. The palo christi (Koeberlinia) is an extreme type. For a crown of thorns no better material could be imagined than this.
On approaching the rocky slopes leading to the higher elevations, a different vegetation is met—different in species, but not in general character. At closer range a distinctively green note in the coloring is appreciated, which at a greater distance was a uniform brown. It is the palo verde (Parkinsonia microphylla), so called in the Spanish on account of the uniform green color of all its members, which gives the impression of verdure. This is a small, somewhat gnarled tree, related to our locust, of the general appearance of a trimmed orchard tree. It is usually leafless, although the younger shoots are sometimes sup-
